THE REMOTE DETECTION OF NATURAL FRACTURES FOR COAL SEAM METHANE

Abstract

Coal seam methane (CSM) is an area of increasing significance to the eastern states of Australia, because by the year 2005, the gas supply from existing fields will be diminishing rapidly. CSM has the economic advantage of being present in seams at easily drillable depths of 300–600 m, and is clean so requires little filtering before use. Since well developed cleat systems are not generally found in Australia due to the presence of high lateral stresses, CSM production is dependent upon permeability, which is reliant on the presence of natural fracture systems.

Work overseas has been progressing on the ability to sense the direction and orientation of fracture systems using three component seismic methods. Our approach has been to use three component methods to sense the presence of fractures, and also to develop new techniques to sense the presence of gas. We use explosive sources rather than controlled shear-wave vibrators. Therefore our methods are relatively inexpensive. Explosive sources generate very strong shear-waves which can be used to observe shear-wave splitting.

This paper discusses a case history of a method to search for fractures in NSW. It shows how the three component seismic method has been used with a conventional explosive source, to indicate the presence of a fracture zone and its orientation, in the Sydney Basin.